The present invention relates to a valve, more particularly a valve having a seat movably attached to the valve casing such that the seat may be self-centered so as to sealingly contact the valve piston.
Operational control of a gas turbine engine is accomplished by control apparatus which may include electrical, electronic, hydraulic and pneumatic components. The control apparatus may also include valves, such as check valves having casings in which a piston is slidably mounted. In order to assure the sealing of the valve, the piston may be spring biased against a valve seat which, as a rule, is fixed in position relative to the valve casing.
Complete sealing is assured only if the piston surface rests against the entire cooperating seat surface. However, machining tolerances in the fabrication of the valve may cause clearances to exist between the piston and the valve casing thereby resulting in imperfect centering of the piston relative to the valve seat. Moreover, if the piston is biased by a spring, the spring may generate a force which is not coaxial with the piston axis. This will cause the force to be unevenly spread along the valve seat, and lateral components of the non-axial piston force may jam the piston against the casing thereby causing it to move further off center relative to the valve seat. The known valve constructions entail the drawbacks of poor sealing between the valve piston and the valve seat in addition to the possibility of jamming the piston within the valve casing.